This invention relates broadly to processes for the removal of radium from acidic solutions and more particularly to processes for effecting such removal by contacting the radium-containing solution with a particulate material.
Uranium usually is extracted from ore by leaching with either sulfuric acid or sodium carbonate. The leaching operation recovers more than 90% of the uranium without dissolving significant quantities of the various radionuclides present in the ore. The resulting leached uranium-ore residues (tailings) constitute a potential radiological hazard requiring perpetual surveillance, the major radiation hazards being due to dissolved radium-226 and its daughter, radon-222.
In the United States, millions of tons of such tailing have accumulated at mill sites. It has been proposed that the tailings may be made environmentally acceptable by leaching them with nitric acid solution to remove the radium-226. Preliminary experiments conducted with 3 M HNO.sub.3 solution indicate that this method is promising, though relatively expensive. The present invention was made in the course of supplementary experiments directed toward finding a suitable process for removing radium-226 from the nitric acid leachate resulting from treatment of the tailings. It was hoped that a process could be found which would be both inexpensive and capable of removing the radium-226 to an extent permitting re-use of the nitric acid in the treatment of uranium-mill tailings.
The known previous art relating to the recovery of radium from uranium-mill waste solutions includes the following article: W. D. Arnold and D. J. Crouse, I & E Process Design and Development, 4(3), 333-337, July 1965. That article describes the adsorption of radium from simulated lime-neutralized acidic waste solutions by adsorption on various inorganic ion exchangers, including natural and synthetic zeolites, barytes, and certain zirconium and barium salts. A few tests were conducted with unneutralized acidic solutions but poor results were obtained. The following reports describe the use of nitric acid solutions for the removal of radium from uranium ore or tailings: 1. ORNL/TM-7065 (January 1980), "Removal of Hazardous Radionuclides from Uranium Ore and/or Mill Tailings", Oak Ridge National Laboratory, Oak Ridge, Tenn. 37830. 2. ORNL/TM-5944 (August 1977), "Nitric Acid Leaching of Radium and Other Significant Radionuclides from Uranium Ores and Tailings", Oak Ridge National Laboratory.
The following report discusses the influence of various burning conditions on the composition and the leaching and sorbate characteristics of coal fly ash: Report DOE/PC/30231--3/(1982), "Leachate-Treatment Technique Utilizing Fly Ash as a Low-Cost Sorbent, Quaterly Progress Report", New Jersey Institute of Technology, Newark, N.J. 07102. The report describes the use of fly ash for the treatment of certain cations and anions originally leached from fly ash in fly ash ponds or in landfill sites. The report does not discuss radium. The use of ash of brown coal (presumably bed ash) to remove .sup.137 Cs and .sup.90 Sr/.sup.90 Y from water is disclosed in the following abstract: SZS-9/68, pp. 14-25, "Use of Kieselguhr, Multiclone Powders and Several Other Adsorbants for Decontamination of Waste Containing .sup.137 Cs and .sup.90 Sr". (Staatliche Zentrale fuer Strahlenschultz, Berlin, East Germany).